We present an effective spectral matching method based on a shape association graph for finding region correspondences between two cel animation keyframes. We formulate the correspondence problem as an adapted quadratic assignment problem, which comprehensively considers both the intrinsic geometric and topology of regions to find the globally optimal correspondence. To simultaneously represent the geometric and topological similarities between regions, we propose a shape association graph (SAG), whose node attributes indicate the geometric distance between regions, and whose edge attributes indicate the topological distance between combined region pairs. We convert topological distance to geometric distance between geometric objects with topological features of the pairs, and introduce Kendall shape space to calculate the intrinsic geometric distance. By utilizing the spectral properties of the affinity matrix induced by the SAG, our approach can efficiently extract globally optimal region correspondences, even if shapes have inconsistent topology and severe deformation. It is also robust to shapes undergoing similarity transformations, and compatible with parallel computing techniques.

Abstract In conventional 2D drawing systems, a drawing usually consists of multiple layers and is composited by rendering layers from back to front. A shape in a higher layer occludes contents in lower layers. However, shapes must have boundaries that form closed regions for occlusion. This limitation causes problems in occlusion resolution. We therefore propose a method to allow users to specify and resolve occlusion in stroke‐based drawing with boundary strokes. Rather than defining shapes, we introduce boundary strokes, which are strokes with occluding sides that work as occluding surfaces. We further introduce a series of user interactions, such as grouping, linking and inverting, on the boundary strokes to realize different occlusion effects. Geometry is then used to find the regions of occluding surfaces to resolve occlusion. The drawings are ready to be coloured, if needed. We extend our method to resolve occlusion in 2D stroke‐based inbetweening. We demonstrate the effectiveness of our method by applying it to resolve occlusion in single drawings and 2D stroke‐based inbetweening.

The heart of every vehicle is its engine. Many factors, either internal or external, contribute to the aircraft engine's durability and lifespan. In this paper, we aim to assist the analyst with a qualitative analysis of the possible external cause of engine failures. We work closely with domain experts to study the domain knowledge, analyze challenging tasks, and abstract user requirements. We present EngineQV, a visualization system that integrates multiple geo-temporal engine-associated records. It provides intuitive exploration and understanding of the data from various aspects. The system features a dynamic query on the datasets and incorporates several customized interactive visualizations. A user may query a certain group of engines or compare multiple engine groups, identify an issue, and find its potential causes. The functionality and usability of EngineQV are evaluated by two case studies, through knowledge discovery from records of a single engine and visual comparison of multiple engines. The validity of the system is confirmed by expert feedback.

This research aims to implement the productive failure teaching concept with interactive learning games as a method to nurture innovative teaching and learning. The research also aims to promote innovative approaches to learning and improving students' learning experience, and their understanding of linked list data structure concepts taught in computer science subjects since students do not widely understand this concept. A 2D bridge building puzzle game, “La Petite Fee Cosmo” was developed to assist students in not only understanding the underlying concepts of the linked list but also foster creative usage of the various functionalities of linked list in diverse situations.

In the visual analysis of high-dimensional data points, star coordinate plot maps the data points into an observable space by conducting a linear combination of radial distributed axes vectors. However, when plotting additional data points which are quite common in an engine performance and simulation model evaluation, the star coordinate is not effective due to undetermined plotting boundary. In response, we propose a geometric algorithm to determine the axis-aligned bounding box, minimum bounding box, and bounding polygon of the star coordinate with an evenly distributed configuration and an arbitrary distributed configuration respectively. These boundaries enable a continuous point rendering that adapts to the screen space boundary. Moreover, the determination of the boundaries provides deeper understandings on the star coordinate plots. Firstly, we amend the expression of the star coordinate by considering the boundaries such that the plotting can be generated reasonably. Secondly, the boundaries provide an objective and quantitative transformation to the widely accepted RadViz measures, in order to exploit the advantages of both. Finally, property analysis, such as the clumping effect of the star coordinate plot, is conducted based on the calculated boundaries.

In this paper, we present a stylization pipeline in 3D object space to emulate traditional charcoal drawing style in real time for cyber arts. First, we introduce an algorithm to produce a rough, grainy charcoal effect based on the lighting available in a 3D scene and the height map of a paper substrate. Then, to further refine the stylized result, we introduce several methods to reproduce some common techniques used in charcoal drawings, such as mixing, smudging and edge softening. The effects can be art-directed in real time to achieve sophisticated charcoal renders that reflect the aesthetic vision of the artist.

In this paper, we present an approach for out-of-core dynamic streaming of a virtual scene. We use the traditional client/server architecture, where the main responsibility of the client application is visualization and interaction, and the main responsibility of the server is accepting and serving requests from the client application. The client will query geometry in the camera proximity to the server and the server will stream geometry (in CityGML format) to the client application. We implement the client application using Unity game engine. Performance comparison between traditional loading and our dynamic streaming are provided. We also show the scalability advantage of our work.

Sketch-based modeling uses freeform strokes as basic modeling metaphor and provides an intuitive way for shape modeling, for instance, for cyberworlds. This paper presents a new method to enhance sketch-based modeling. The core idea of the method is to enhance the sketching process by allowing the user to iteratively sketch to progressively create initial shapes that interpolate the sketched strokes. This process considers all the sketches and the up-to-date constructed 3D shape, which enables the user to be aware of the shape of the sketched model. The key underlying technique that supports this process is a novel surface construction algorithm, which generates 3D triangular mesh models with gradual shape changes during iterative sketching. Experiments demonstrate that the presented method can allow users to intuitively and flexibly create and edit 3D models even with complex topology, which is usually difficult in existing sketch-based modeling systems.

Relocalization is one of the necessary modules for mobile robots in long-term autonomous movement in an environment. Currently, visual relocalization algorithms mainly include feature-based methods and CNN-based (Convolutional Neural Network) methods. Feature-based methods can achieve high localization accuracy in feature-rich scenes, but the error is quite large or it even fails in cases with motion blur, texture-less scene and changing view angle. CNN-based methods usually have better robustness but poor localization accuracy. For this reason, a visual relocalization algorithm that combines the advantages of the two methods is proposed in this paper. The BoVW (Bag of Visual Words) model is used to search for the most similar image in the training dataset. PnP (Perspective n Points) and RANSAC (Random Sample Consensus) are employed to estimate an initial pose. Then the number of inliers is utilized as a criterion whether the feature-based method or the CNN-based method is to be leveraged. Compared with a previous CNN-based method, PoseNet, the average position error is reduced by 45.6% and the average orientation error is reduced by 67.4% on Microsoft's 7-Scenes datasets, which verifies the effectiveness of the proposed algorithm.

Abstract Stroke correspondence construction is a precondition for vectorized 2D animation inbetweening and remains a challenging problem. This paper introduces the FTP‐SC, a fuzzy topology preserving stroke correspondence technique, which is accurate and provides the user more effective control on the correspondence result than previous matching approaches. The method employs a two‐stage scheme to progressively establish the stroke correspondence construction between the keyframes. In the first stage, the stroke correspondences with high confidence are constructed by enforcing the preservation of the so‐called “fuzzy topology” which encodes intrinsic connectivity among the neighboring strokes. Starting with the high‐confidence correspondences, the second stage performs a greedy matching algorithm to generate a full correspondence between the strokes. Experimental results show that the FTP‐SC outperforms the existing approaches and can establish the stroke correspondence with a reasonable amount of user interaction even for keyframes with large geometric and spatial variations between strokes.

In our turbine performance assessment, we need to provide an effective visual analytics tool in handling high-dimensional datasets. We have employed RadViz in 2D exploratory data analysis. However, with the increase of dataset size and dimensionality, the clumping of projected data points towards the origin in RadViz causes low space utilization, which largely degenerates the visibility of the feature characteristics. In this study, to better evaluate the hidden patterns in the center region, we propose histogram-based techniques to manipulate the radial distribution of data points in RadViz. We present RadViz in the polar coordinate system for convenient radial operations. Based on this, we define the radial equalization method to automatically spread out the frequency and the radial specification method to shape the distribution based on the user's requirement. Furthermore, we utilize the information in high-dimensional space as histogram and reference point to design and control the radial distribution of RadViz. Computational experiments have been conducted on turbine performance simulation data. Our proposed techniques are shown advantageous in query result display and outlier detection with a set of high-dimensional datasets.

Interpolation is the most executed operation and one of the main bottlenecks in embedded imaging, registration, and rendering systems. Existing methods either lack parallelization and scalability capabilities or are too computationally complex to execute efficiently. Acknowledging that improving execution time leads to degradation in image quality, we formulate a novel Negative Squared Distance (NSD) interpolation method that exhibits excellent performance by exploiting Look-Up Table (LUT) optimization for Field Programmable Gate Array (FPGA) speedup, with a balanced trade-off in quality in our embedded endomicroscopic imaging system. Quantitative analysis on performance and resource utilization of NSD against existing methods is reported through an implementation on a Xilinx ML605 platform. Functional validation using practical image resizing and rotation applications to compare qualitative performance against existing algorithms is performed and presented with visual and numerical results. Our method is shown to have a smaller design size and produces a maximum throughput of over twofold against trilinear interpolation with on-par image quality as the baseline method.

Physically based deformable models have been a hot topic in the computer graphics and visualization community. However, most of the implemented models work only for isotropic materials, leaving the more general anisotropic materials less studied. We look into the challenging issues in dynamics simulation and real time visualization for anisotropic materials, and present our theoretic and practical work along the way to provide an ultimate solution to deformation with such materials. First, our models are based on continuum mechanics and approximated by the Finite Element Method, and different approaches such as co rotated, invertible, and total Lagrangian explicit dynamics. Secondly, for controls of the deformation, we have focused on materials that have their own internal structures (fibers) that determine the dynamics behaviors. We propose a fibers incorporated deformable model that can approximate the anisotropic elastic material properties. The orientation information is combined into the existing deformable models by element transformations along the given directions, which provide a control of the desired deformation. Thirdly, constraints for the strain density in linear elastic models are analyzed, and a positive-definite elasticity tensor is derived for an anisotropic material. Fourthly, an orthotropic deformation controlling frame-field is conceptualized and the frame construction tool is developed for the user to define the desired material properties. A quaternion Laplacian smoothing algorithm is designed for propagating the rotation minimization frames into the entire object. And finally, the co rotational linear FEM model is coupled with the orthotropic frame-field to realize a dynamics system, which can deal with large anisotropic deformations.

Modern computer graphics applications commonly feature very large virtual environments and diverse characters which perform different kinds of motions. To accelerate path planning in such a scenario, we propose the subregion graph data structure. It consists of subregions, which are clusters of locally connected waypoints inside a region, as well as subregion connectivities. We also present a fast algorithm to automatically generate a subregion graph from an enhanced waypoint graph map representation, which also supports various motion types and can be created from large virtual environments. Nevertheless, a subregion graph can be generated from any graphbased map representation. Our experiments show that a subregion graph is very compact relative to the input waypoint graph. By firstly planning a subregion path, and then limiting waypoint-level planning to this subregion path, over 8 times average speedup can be achieved, while average length ratios remain as low as 102.5%.

Recently, points of interest (POIs) recommendation has evolved into a hot research topic with real-world applications. In this paper, we propose a novel semantics-enhanced density-based clustering algorithm SEM-DTBJ-Cluster, to extract semantic POIs from GPS trajectories. We then take into account three different factors (popularity, temporal and geographical features) that can influence the recommendation score of a POI. We characterize the impacts caused by popularity, temporal and geographical information, by using different scoring functions based on three developed recommendation models. Finally, we combine the three scoring functions together and obtain a unified framework PTG-Recommend for recommending candidate POIs for a mobile user. To the best of our knowledge, this work is the first that considers popularity, temporal and geographical information together. Experimental results on two real-world data sets strongly demonstrate that our framework is robust and effective, and outperforms the baseline recommendation methods in terms of precision and recall.

Triangle meshes are used in representation of 3D geometric models, and they are subject to various visual distortions during geometrical processing and transmission. In this study, we propose a novel objective quality assessment method for 3D meshes based on curvature information; according to characteristics of the human visual system (HVS), two new components including visual masking and saturation effect are designed for the proposed method. Besides, inspired by the fact that the HVS is sensitive to structural information, we compute the structure distortion of 3D meshes. We test the performance of the proposed method on three publicly available databases of 3D mesh quality evaluation. We rotate among these databases for parameter determination to demonstrate the robustness of the proposed scheme. Experimental results demonstrate that the proposed method can predict consistent results in terms of correlation to the subjective scores across the databases.

Curves and lines are fundamental elements in animation sketches. To sketch an animation sequence manually would be a very laborious task. Also to enable these curves and lines to be manipulated efficiently would be very important for productivity. Here we propose a 3D model-based approach for generating 2D and 3D curves from a 3D animation sequence. We introduce an automatic method to extract 3D and 2D feature curves from the 3D animation through curve tracing, matching and evolving. All the 3D and 2D curves extracted are spatially and temporally coherent. Moreover, the geometrical relationship between the 2D and 3D curves are established. The curves are processed and vectorized to allow artists to intuitively edit and author the animation by manipulating the 3D and 2D features. By using distinct points on the feature curves as basis, we apply the radial basis function to deform the entire geometry of the animated model across the entire sequence. The result showed that our method has promising potential to make the animation process to be more time efficient.

Prediction of the 3D structure of protein-protein complexes is crucial for understanding the biological system of life and thus for designing drugs. However it is a challenging problem due to the flexibility of the backbone and side-chains of the receptor and ligand. In this paper, we present a new framework for fast and flexible protein-protein docking based on geometric and physicochemical complementarity. In our approach, we segment the protein surfaces into several local surface patches and describe the effect of side-chain flexibility on each patch by sampling the space of conformation of its side-chains. Then the geometric complementarity can be determined by matching these surface patches. During the matching, we propose a new 3D shape descriptor, Spherical Harmonics Descriptor. The main property of the Spherical Harmonics Descriptor is rotation invariance which avoids taking an exhaustive set of rotations for each pair of patches. Thus, the geometric complementarity matching problem is simplified to a histogram matching problem. This can greatly reduce the computational cost. Finally, the docking candidates are evaluated by a scoring function which can accommodate geometric complementarity and physicochemical matching. The experimental results demonstrate the high efficiency and accuracy of the proposed method.

Curve blending is an essential task in geometric modeling, while a ball B-spline curve (BBSC) has its advantages in representing freeform tubular objects. This paper proposes a blending algorithm for ball B-Spline curve with G2 continuity, which is used to describe the smoothness of the joint point. An original BBSC is extended smoothly to join another one, such that no additional blending curve is created and the two original curves are not changed. The shape of the extended curve is then determined by minimizing strain energy. The corresponding scalar function of the control balls is determined through applying G2-continuity conditions to the scalar function. In order to ensure the radii of the control balls are positive, we make a decision about the range of the G2-continuity parameter and then determine it by minimizing the strain energy in the affected area. The experiment results demonstrate our method for blending BBSC is effective. Moreover, some G2 blending results of the BBSC in simulating the tubular objects are given.

Curve extension is a useful function in CAD systems. Disk B-Spline curve has its distinct advantages in representing a 2D region. This paper presents an algorithm for extending the disk B-Spline curve. A disk Bezier segment is used to construct the extending part and G2-continuity can be used to describe the smoothness of the joint disk. Fairness of the extending disk Bezier segment is achieved by minimizing an energy objective function. New control disks are computed by unclamping algorithm to represent the whole extended disk B-Spline curve. The experimental results demonstrate the effectiveness of our method.

Given a set of moving clients as well as their friend relationships, a road network, and a distance threshold per friend pair, the proximity detection problem in road networks is to find each pair of friends such that the road network distance between them is within the given threshold. The problem of proximity detection is often encountered in friend-locator applications and massively multiplayer online games. Because of the limited battery power and bandwidth, it is better to develop a solution which incurs less communication cost. Hence, the main objective of this problem is to reduce the total communication cost. However, most of the existing proximity detection solutions focus on the Euclidean space but cannot be used in road network space; the solutions for road networks incur substantial communication costs. Motivated by this, we propose two types of solutions to solve the proximity detection problem in road networks. In the first type of solution, each mobile client is assigned with a mobile region of a fixed size. We design algorithms with a fixed radius for the client and server respectively, with the purpose of reducing unnecessary probing messages and update messages. Second, we present a self-tuning policy to adjust the radius of the mobile region automatically to minimize the communication cost. Experiments show that our second type of solution works efficiently and robust with a much lower communication cost with respect to various parameters. In addition, we present our server-side computational cost optimization techniques to reduce the total computational cost.

For high-quality image rendering using Monte Carlo methods, a large number of samples are required to be computed for each pixel. Adaptive sampling aims to decrease the total number of samples by concentrating samples on difficult regions. However, existing adaptive sampling schemes haven't fully exploited the potential of image regions with complex structures to the reduction of sample numbers. To solve this problem, we propose to exploit uncertainty masking in adaptive sampling. Experimental results show that incorporation of uncertainty information leads to significant sample reduction and therefore time-savings.

In this work, we propose a method to detect visually salient objects in computer synthesized images from 3D meshes. Different from existing detection methods on graphic saliency which compute saliency based on pixel-level contrast, the proposed method computes saliency by measuring object-level contrast of each object to the other objects in a rendered image. Given a synthesized image, the proposed method first extracts dominant colors from each object, and represents each object with the dominant color descriptor (DCD). Saliency is measured as the contrast between the DCD of the object and the DCDs of its surrounding objects. We evaluate the proposed method on a data set of computer rendered images, and the results show that the proposed method obtains much better performance compared with existing related methods.

Abstract Producing traditional animation is a laborious task where the key drawings are first drawn by artists and thereafter inbetween drawings are created, whether it is by hand or computer‐assisted. Auto‐inbetweening of these 2D key drawings by computer is a non‐trivial task as 3D depths are missing. An alternate approach is to generate all the drawings by extracting lines directly from animated 3D models frame by frame, concatenating and rendering them together into an animation. However, animation quality generated using this straightforward method bears two problems. Firstly, the animation contains unsatisfactory visual artifacts such as line flickering and popping. This is especially pronounced when the lines are extracted using high‐order derivatives, such as ridges and valleys, from 3D models represented in triangle meshes. Secondly, there is a lack of temporal continuity as each drawing is generated without taking its neighboring drawings into consideration. In this paper, we propose an improved approach over the straightforward method by transferring extracted 3D line drawings of each frame into individual 3D lines and processing them along the time domain. Our objective is to minimize the visual artifacts and incorporate temporal relationship of individual lines throughout the entire animation sequence. This is achieved by creating correspondent trajectory of each line from each frame and applying global optimization on each trajectory. To realize this target, we present a fully automatic novel approach, which consists of (1) a line matching algorithm, (2) an optimizing algorithm, taking into account both the variations of numbers and lengths of 3D lines in each frame, and (3) a robust tracing method for transferring collections of line segments extracted from the 3D models into individual lines. We evaluate our approach on several animated model sequences to demonstrate its effectiveness in producing line drawing animations with temporal coherence.

Compared to monocular pose tracking, 3D articulated body pose tracking from multiple cameras can better deal with self-occlusions and meet less ambiguities. Though considerable advances have been made, pose tracking from multiple images has not been extensively studied: very seldom existing work can produce a solution comparable to that of a marker-based system which generally can recover accurate 3D full-body motion in real-time. In this paper, we present a multi-view approach to 3D body pose tracking. We propose a pose search method by introducing a new generative sampling algorithm with a refinement step of local optimization. This multi-layer search method does not rely on strong motion priors and generalizes well to general human motions. Physical constraints are incorporated in a novel way and 3D distance transform is employed for speedup. A voxel subject-specific 3D body model is created automatically at the initial frame to fit the subject to be tracked. We design and develop the optimized parallel implementations of time-consuming algorithms on GPU (Graphics Processing Unit) using CUDA (Compute Unified Device Architecture), which significantly accelerates the pose tracking process, making our method capable of tracking full body movements with a maximum speed of 9 fps. Experiments on various 8-camera datasets and benchmark datasets (HumanEva-II) captured by 4 cameras demonstrate the robustness and accuracy of our method.

In the fields of computer vision, multiple object tracking is an active research area. It is a challenging problem mainly due to the frequent occlusions and interactions that happen between the multiple targets. We formulate the multiple interaction problem as an optimization problem and explore Particle Swarm Optimization (PSO) algorithm for the optimal solution. To tackle the problem of premature convergence, we present a new hybrid PSO that incorporates a differential evolution mutation operation with a Gaussian based PSO. Furthermore, by exploiting the specific structure of multiple object interactions, we introduce a cooperative strategy into the proposed PSO for more efficient searching and for conquering the curse of dimensionality. With patch-based observation models, our method can robustly handle significant occlusions and interactions.

Our research focuses on the problem of path planning, which often occurs in virtual world applications. We propose an automatic generation of enhanced waypoint graph, which is a graph data structure consisting of point nodes, which describe the corner features in the virtual world, as well as edges connecting those nodes. Given a polygon soup representation of a virtual world, for every character radius, the proposed algorithm starts by constructing a discrete distance field, consisting of regularly sampled points in 3D space. Corner detection and clustering are then done with respect to the points whose distance values are slightly larger than the character size to get the waypoints. These waypoints are further sparsely connected using traversability test, taking into account their distances to nearby obstacles. The resulting enhanced waypoint graph is sparse but has regularly distributed edges emanating from each waypoint. In addition, the graph is also able to handle different types of motions for characters with various sizes.

Tracking of 3D human body movement from multiple camera video streams is an important problem in the domain of computer vision. In this paper we perform body pose tracking in 3D space using 3D data reconstructed at every frame. We present an efficient GPU-based method for 3D reconstruction of the real world dynamic scenes. Besides volumetric reconstruction, we propose to compute view-independent 3D optical flow (i.e., scene flow) in combination with volumetric reconstruction, and have attained efficient scene flow estimation using GPU acceleration. Body pose estimation starts from a deterministic prediction based on scene flow, and then uses a multi-layer search algorithm involving stochastic search and local optimization. We design and parallelize the PSO-based (particle swarm optimization) stochastic search algorithm and 3D DT (distance transform) computation of the pose estimation method on GPU. To the end, our system can reach efficient and robust body pose tracking.

How do we retrieve cartoon characters accurately? Or how to synthesize new cartoon clips smoothly and efficiently from the cartoon library? Both questions are important for animators and cartoon enthusiasts to design and create new cartoons by utilizing existing cartoon materials. The first key issue to answer those questions is to find a proper representation that describes the cartoon character effectively. In this paper, we consider multiple features from different views, i.e., color histogram, Hausdorff edge feature, and skeleton feature, to represent cartoon characters with different colors, shapes, and gestures. Each visual feature reflects a unique characteristic of a cartoon character, and they are complementary to each other for retrieval and synthesis. However, how to combine the three visual features is the second key issue of our application. By simply concatenating them into a long vector, it will end up with the so-called "curse of dimensionality," let alone their heterogeneity embedded in different visual feature spaces. Here, we introduce a semisupervised multiview subspace learning (semi-MSL) algorithm, to encode different features in a unified space. Specifically, under the patch alignment framework, semi-MSL uses the discriminative information from labeled cartoon characters in the construction of local patches where the manifold structure revealed by unlabeled cartoon characters is utilized to capture the geometric distribution. The experimental evaluations based on both cartoon character retrieval and clip synthesis demonstrate the effectiveness of the proposed method for cartoon application. Moreover, additional results of content-based image retrieval on benchmark data suggest the generality of semi-MSL for other applications.

We present a markerless system for recovering 3D full-body motion from multiple image sequences. Our approach supports robust pose tracking from 3D data as well as automatic body model acquisition. For initialization, a subject-specific voxel body model that fits well to the shape of the subject being tracked is automatically created from the beginning volume. Then for pose recovery, the voxel body model is matched to the image features via a hierarchical pose search method. We use a new particle based stochastic search algorithm and introduce a robust metric, which is incorporated with joint limits, physical constraints and fuses multiple 3D cues involving volume spatial and 3D scene flow motion information. Results on several complex multiple sequences show the robustness and effectiveness of our approach.

Line drawings are an effective way to convey shapes in a relatively succinct manner by ignoring the less important or distracting details. In the past decade, many promising computer-generated line drawing algorithms have been proposed, which can be roughly classified into two categories: object-space and image-space.

Abstract Stroke correspondence construction is a precondition for generating inbetween frames from a set of key frames. In our case, each stroke in a key frame is a vector represented as a Disk B‐Spline Curve (DBSC) which is a flexible and compact vector format. However, it is not easy to construct correspondences between multiple DBSC strokes effectively because of the following points: (1) with the use of shape descriptors, the dimensionality of the feature space is high; (2) the number of strokes in different key frames is usually large and different from each other and (3) the length of corresponding strokes can be very different. The first point makes matching difficult. The other two points imply ‘many to many’ and ‘part to whole’ correspondences between strokes. To solve these problems, this paper presents a DBSC stroke correspondence construction approach, which introduces a manifold learning technique to the matching process. Moreover, in order to handle the mapping between unequal numbers of strokes with different lengths, a stroke reconstruction algorithm is developed to convert the ‘many to many’ and ‘part to whole’ stroke correspondences to ‘one to one’ compound stroke correspondence.

Correspondence construction of objects in key frames is the precondition for inbetweening and coloring in 2-D computer-assisted animation production. Since each frame of an animation consists of multiple layers, objects are complex in terms of shape and structure. Therefore, existing shape-matching algorithms specifically designed for simple structures such as a single closed contour cannot perform well on objects constructed by multiple contours with an open shape. This paper introduces a semisupervised patch alignment framework for complex object correspondence construction. In particular, the new framework constructs local patches for each point on an object and aligns these patches in a new feature space, in which correspondences between objects can be detected by the subsequent clustering. For local patch construction, pairwise constraints, which indicate the corresponding points (must link) or unfitting points (cannot link), are introduced by users to improve the performance of correspondence construction. This kind of input is convenient for animation software users via user-friendly interfaces. A dozen of experimental results on our cartoon data set that is built on industrial production suggest the effectiveness of the proposed framework for constructing correspondences of complex objects. As an extension of our framework, additional shape retrieval experiments on MPEG-7 data set show that its performance is comparable with that of a prominent algorithm published in T-PAMI 2009.

This paper presents a sketch-based modeling system with auxiliary planes as references for 3D freeform shape design. The user first creates a rough 3D model of arbitrary topology by sketching some contours of the model. Then the user can use sketching to perform deformation, extrusion, etc, to edit the model. To regularize and interpret the user's inputs properly, we introduce some rules for the strokes into the system, which are based on both the semantic meaning of the sketched strokes and human psychology. Unlike other sketching systems, all the creation and editing operations in the presented system are performed with reference to some auxiliary planes that are automatically constructed based on the user’s sketches or default settings. The use of reference planes provides a heuristic solution to the problem of ambiguity of 2D interface for modeling in 3D space. Examples demonstrate that the presented system can allow the user to intuitively and intelligently create and edit 3D models even with complex topology, which is usually difficult in other similar sketch-based modeling systems.

We present an interactive framework for rapid 3D reconstruction of objects from sets of photographs. Our framework implements advanced 2D image-based modeling techniques that accurately compute geometries of digital photorealistic 3D models in a rapid and robust method. It is implemented in an application tool to assist users to perform feature detection, matching and meshing. Our system demonstrates that with a few user's intervention through our application tool, efficient generation of 3D object models can be generated from a set of photos.

Abstract To reduce tedious works in cartoon animation, some computer‐assisted systems including automatic inbetweening and cartoon reusing systems have been proposed. In existing automatic inbetweening systems, accurate correspondence construction, which is a prerequisite for inbetweening, cannot be achieved. For cartoon reusing systems, the lack of efficient similarity estimation method and reusing mechanism makes it impractical for the users. The Transductive Graph based Cartoon Synthesis (TGCS) approach proposed in this paper aims at synthesizing smooth cartoons from the existing data. In this approach, the similarity between cartoon frames can be accurately evaluated by calculating the distance based on local shape context, which is rotation, and scaling invariant. According to the similarity, the label propagation based graph transduction method is adopted to generate cartoon clips, which is smoother than the clips generated by the shortest path method used in previous cartoon reusing approaches. Besides, the synthesized cartoon clips can be applied in accurate correspondence building, based on which the inbetweening method can be used to refine the results. Experimental results on our cartoon dataset suggest the effectiveness of the proposed approach for cartoon synthesis. Additional experiments on correspondence show our approach's performance on accurate correspondence building. Copyright © 2010 John Wiley & Sons, Ltd.

In this paper, we propose a feature-based registration algorithm for the confocal fluorescence images captured by an endomicroscopy system. We first extract a number of feature points from the endomicroscopy images by applying the binarization-thinning process and using the Rutovitz crossing number. These feature points are then post-processed to eliminate the spurious ones. After that we use the purified feature points to complete the image registration between every two consecutive slice images. The aligned image stack will be finally utilized to reconstruct and visualize the 3D structure of the living cell and tissue in real time, which provides the opportunity for the clinicians to diagnose various diseases including the early-stage cancers.

Plankton image classification plays an important role in ocean biological research. In this paper, we present an approach based on the bagging technique to classify the marine plankton images captured by the shadowed image particle profiling and evaluation recorder. The difficulty of such classification is multifold because the data set is much noisier, and the plankton images are deformable, projection-variant, and often in partial occlusion. In addition, the images in our experiments are binary, thus are lack of pixel-depth information. By random sampling with replacement on the original training set, a number of independent bootstrap replicates are generated. Using these replicates as new training sets, we construct multiple classifiers that are complementary of one another. While such individual classifiers are less effective than a single classifier trained on the whole training set, the fusion of them using majority voting produces an improved tenfold cross-validation accuracy by more than 93%.

In-between creation in traditional cel animation based on the hand-drawn key-frames is a fundamental element for the actual production and plays a symbolic role in an artistic interpretation of the scene. To create impressive in-betweens, however, animators are required to be skilled for hair animation creation. In the traditional cel animation, hair motions are generally used to express a character's affective change or showing environment condition. Despite this usability and importance, the hair motion is drawn relatively simply or is not animated at all because of the lack of skilled animators and time constraints in cel animation production. To assist this production process, P. Noble and W. Tang [Noble and Tang. 2004], and Sugisaki et al. [Sugisaki et al. 2006] introduced certain ways to create hair motion for cartoon animations. Both of them created the hair motion based on 3D simulation that is applied to the prepared 3D character model. In this paper, we introduce an in-between creation method, specialized for hair based on dynamic simulation, which does not need any 3D character model. Animators can create in-between frames for hair motion by setting a few parameters, and then our method automatically select the best in-between frames based on the specified frame number by animator. The advantage of our method is to create in-between frames for hair motion by applying simulation model to key-frames. Obviously, the key-frame images do not have any depth. In fact, our method can directly utilize the hand-drawn key-frames which are drawn by animators in CACAni (Computer-Assisted Cel Animation) system [CACAni Website].

Abstract In this paper, we propose an instant shadow generation technique for 2D animation, especially Japanese Anime. In traditional 2D Anime production, the entire animation including shadows is drawn by hand so that it takes long time to complete. Shadows play an important role in the creation of symbolic visual effects. However shadows are not always drawn due to time constraints and lack of animators especially when the production schedule is tight. To solve this problem, we develop an easy shadowing approach that enables animators to easily create a layer of shadow and its animation based on the character's shapes. Our approach is both instant and intuitive. The only inputs required are character or object shapes in input animation sequence with alpha value generally used in the Anime production pipeline. First, shadows are automatically rendered on a virtual plane by using a Shadow Map1based on these inputs. Then the rendered shadows can be edited by simple operations and simplified by the Gaussian Filter. Several special effects such as blurring can be applied to the rendered shadow at the same time. Compared to existing approaches, ours is more efficient and effective to handle automatic shadowing in real‐time. Copyright © 2009 John Wiley & Sons, Ltd.

Animation created using computer graphics is seen through a viewport which is dictated by what the director or producer wants the consumer to watch. This includes the usual cinematography to bring out the best dramatical effects. Consumers, however, do not have a choice but to passively receive the imagery that unfolds through the screen. This paper proposes the concept of a consumer editable animation, which aims to provide consumers with the flexibility to change attributes of the scene and also to decide what and how they want to view the final animation. Another key point is that all data are vector-based and the animation sequences are therefore rescalable.

Skinning existing animation frames or examples is exploited actively to find the most suitable scheme that is capable of capturing deformations from given mesh sequences. It is necessary to approximate joint transformations by a fitting algorithm that usually involves solving a large scale linear system. In this paper, we reduce the dimensions of the linear system substantially by representing example meshes as progressive decimated models. These models are reconstructed from augmented deformation sensitive decimation (ADSD) that is able to handle large deformations while maintaining connectivity relationship throughout all example meshes. We also show that skinning can be propagated to decimated models, which allows animations to be scalable to specific applications with varied requirements of qualities.

This paper proposes a bidirectional modeling approach. It aims to assist online collaboration on 2D to 3D modeling. Two "worlds" of modeling are proposed in our pipeline. A free-form 3D model can be generated in the "creation world" (CW). Then models are transferred to another "world", the "viewing world" (VW), and integrated with existing virtual scene. Models in the "viewing world" can also be transferred back to the "creation world" for further refinement. All operations performed in the "creation world" are based on our sketch-up technique, which is a new method to accomplish 2D to 3D reconstruction. In this method, 3D models are created through a traditional and intuitive way, "painting", with a mouse/stylus. The approach proposed in this paper can be applied to help online e-edutainment and e-learning applications. It is expected to help multi-user modeling and geometric learning online. With our method, collaborative modeling on the Web can be carried out in an easy and intuitive manner.

This paper presents a method to extract skeletons using examples. Our method is based on the observation that many deformations in real world applications are isometric or near isometric. By taking advantage of the intrinsic property of harmonic 1-form, i.e., it is determined by the metric and independent of the resolution and embedding, our method can easily find a consistent mapping between the reference and example poses which can be in different resolutions and triangulations. We first construct the skeleton-like Reeb graph of a harmonic function defined on the given poses. Then by examining the changes of mean curvatures, we identify the initial locations of joints. Finally we refine the joint locations by solving a constrained optimization problem. To demonstrate the efficacy of our method, we apply the extracted skeletons to pose space deformation and skeleton transfer.

This paper proposes a new skeleton based parametric representation of freeform shell-like solid objects — Ball B-Spline Surfaces (BBSSs) and their fundamental properties and algorithms. BBSSs are generalizations of ball B-Spline curve from one parameter variable to two parameter variables. BBSSs directly define objects in B-Spline form, unlike a procedure method like sweeping. BBSSs describe not only every point inside 3D solid objects, but also provides their center surface (skeleton). So the representation is more flexible for modeling, manipulation and deformation.

This paper proposes a parametric solid representation of freeform tubular objects - Ball B-Spline Curves (BBSCs), which are skeleton based parametric solid model. Their fundamental properties, algorithms and modeling methods are investigated. BBSC directly defines objects in B-Spline function form (not a procedure method, like sweeping), that uses control ball instead of control point in B-Spline curve. BBSC describes not only every point inside 3D solid objects, but also provides its center curve in B-Spline form directly. So the representation is more flexible for modeling, manipulation and deformation.

Conveying shape using feature lines is an important visualization tool in visual computing. The existing feature lines (e.g., ridges, valleys, silhouettes, suggestive contours, etc.) are solely determined by local geometry properties (e.g., normals and curvatures) as well as the view position. This paper is strongly inspired by the observation in human vision and perception that a sudden change in the luminance plays a critical role to faithfully represent and recover the 3D information. In particular, we adopt the edge detection techniques in image processing for 3D shape visualization and present Photic Extremum Lines (PELs) which emphasize significant variations of illumination over 3D surfaces. Comparing with the existing feature lines, PELs are more flexible and offer users more freedom to achieve desirable visualization effects. In addition, the user can easily control the shape visualization by changing the light position, the number of light sources, and choosing various light models. We compare PELs with the existing approaches and demonstrate that PEL is a flexible and effective tool to illustrate 3D surface and volume for visual computing.

An explicit constraint is introduced into the Lucas-Kanade gradient based block motion model. This constraint helps the estimation process to consider surrounding motion vectors during its calculation. Consequently a better motion field can be produced than that by the original block motion model. Further, a discontinuity adaptive function is introduced into the Lucas-Kanade equation, which helps to preserve the discontinuities of motion fields

Abstract Disk B‐spline curve (DBSC) is previously proposed for drawing and animation. To generate inbetweens, linear interpolation is applied between points evenly taken in parametric domain of two DBSCs without incorporating characteristics of shape or motion, which results in distortion and unrealistic motion in animation. In this paper, more information in keyframes is extracted and utilized in inbetween generation. Points with high curvature are computed and corresponded between strokes in interpolation, which preserves features of strokes in animation. In addition, global motion of a character or its various components is estimated and interpolated as well, which retains the shapes during the motion. By applying the information to interpolation, the distortion is eliminated and smoother sequence of animation is achieved. Copyright © 2006 John Wiley & Sons, Ltd.

for cyberworlds' sessions of the conference.

Abstract This paper proposes a Hierarchical Region Matching (HRM) approach for computer‐assisted auto coloring. The region‐level analysis in traditional 2D animation is expanded into several component levels with a novel hierarchization method. With the hierarchy, various region matching algorithms can be applied from the first/highest to the last/lowest component level. HRM improves the matching accuracy and may deal with matching errors caused by occlusion, thus making the matching more robust, as verified by the results. Copyright © 2005 John Wiley & Sons, Ltd.

Automatic inbetweening is one of the main focuses in computer assisted cel animation as inbetweening process is traditionally time-consuming and labor-intensive in the production of cartoon animation. Most previous work demand either lots of modeling or working with complicated programs and their interfaces, which do not take much animator's expertise into consideration, as animators are usually more capable of drawing pictures on the paper than programming with computer. An approach proposed in this paper aims to provide an easy-to-use system which automatically models key frames "on the fly " and interpolates them in several layers, including object size and position, line curvatures and curve texture in order to preserve artistic style of the hand-drawn key frames and make the motion smooth and natural. Without much user interaction and complicated program interface the system may be tuned, uploaded into the Web so that not only professional artists but those who are interested in cartoon but don't have much time or skill on drawing frames or inexperienced at using computer, like students, free-lance animators, etc. may benefit from using the system, for example, creating animation clips for the Web. The results show that the algorithm works well although it leaves areas for further research to extend and improve the algorithm to work with as many different types of key frames as possible.

In this paper, a system named IVS (Interactive Virtual Studio), which integrates low-level (feature extraction and ordering), mid-level (camera parameters estimation and evaluation), high-level (object recognition and reconstruction), and graphics techniques, is presented. The purpose of IVS is to integrate computer generated animation with real image sequence seamlessly. With minimum human intervention, IVS is an off-line postprocessing system that operates on a real world sequence in which a known object is tracked. The camera pose in each frame is recovered from which the camera trajectory is reconstructed. Firstly, object features are extracted from the environment and correspondence between the extracted shape and a shape from a database is solved by an SVD (Singular Value Decomposition) based technique. Secondly, SFSM (Structure from Simulated Motion) is used for object recognition and the information is used for reconstruction of the 3D object contained in the image. An evaluation mechanism is introduced to provide feedback and reduce the registration error. In the last stage of the processing, virtual graphics objects are imported to interact with the real image sequence. While the concept of developing such a system is not new, the various novel techniques we incorporated into IVS make it different.

Computer-assisted auto coloring (CAAC) has great potential in terms of lowering production cost and saving time in cel animation production. In this paper, a novel approach to automatically color the animation character of line drawings based on region matching and master frames is proposed. Firstly, some important attributes of a region such as curve length, character points, area etc. are investigated. Then, based on these attributes, a detailed process of region matching is presented followed by the coloring process. The results show that our approach can straightforwardly handle most cases, hence the aim of saving time and labor is realized.